Bullets and Bunkum:The futility of 'Ballistic Fingerprinting'

In the wake of the Washington, D.C., sniper
attacks, many are viewing ballistic fingerprinting as a magic crime-solving tool.
According to the pro-gun-control Brady Campaign, such a system "would have solved
[the sniper case] after the first shooting"; a Washington Post columnist
calls it a "common-sense measure"; and many politicians are jumping on board,
including New York Democratic senator Charles Schumer and Maryland Democratic
gubernatorial nominee Kathleen Kennedy Townsend.

Unfortunately, the issue is not so simple: By draining resources away from other police
activities and making it costly for law-abiding citizens to own guns, ballistic
fingerprinting could end up actually increasing crime.

The physics of ballistic fingerprinting are straightforward. When a bullet travels
through the barrel of a gun, the friction creates markings on the bullet. If the gun is
new, imperfections in the way the barrel is drilled can produce different markings on the
bullet; such imperfections are most noticeable in inexpensive guns. (This poses an irony
for gun controllers, who push for laws that ban inexpensive guns.) In older guns, the
bullets' friction through the barrel can cause more noticeable wear marks that help
differentiate between guns. Many other factors influence the particular markings left on
the bullets — for instance, how often the gun is cleaned and what brand of cartridge
is used.

Precisely because friction causes wear, a gun's ballistic fingerprint changes over time
— making it drastically different from such forensic evidence as human fingerprints
or DNA. The recording of a child's fingerprints or DNA still allows for identification
much later in life; the same is not true of the bullet markings. A ballistic fingerprint
is less like a human fingerprint than it is like the tread on a car tire.

Brand-new tires are essentially identical, so new-tire tracks at crime scenes leave
investigators with pretty limited information. Unless there happens to be a particular
imperfection, only the brand and model of the tire can be identified. Imprints on bullets
are similar. When a bullet is fired from a new gun, investigators can typically identify
only the type of ammunition and the type of gun.

Over time, though, friction causes the tread on tires to wear. It would be easy to take
the tire tracks left at a crime scene and match them with a suspected criminal's car; but
the more the car is driven after the crime, the harder it is to match the tire tracks left
at the scene to the tires when they are eventually found. Similarly, the greatest friction
on a gun occurs when the gun is first fired — and that dramatically reduces the
usefulness of recording the gun's ballistic fingerprint when it is purchased.

Moreover, ballistic fingerprinting can be thwarted by replacing the gun's barrel —
just as criminals can foil tire-matching by simply replacing their tires. In general, the
markings on bullets can be altered even more quickly and easily than the tread marks on
tires: Scratching part of the inside of a barrel with a nail file would alter the bullet's
path down the barrel and thus change the markings. So would putting toothpaste on a bullet
before firing it.

Ballistic fingerprinting faces other difficulties. For example, even if the gun was not
used much between the time the ballistic fingerprint was originally recorded and the time
the crime occurred, police still have to be able to trace the gun from the original owner
to the criminal — but only 12 percent of guns used in crime are obtained by the
criminal through retail stores or pawn shops. The rest are virtually impossible to trace.

So far only Maryland and New York have started recording the ballistic fingerprints of
all new handguns sold. While Maryland's program technically started in January 2001, the
cost of implementing the program made it unprofitable for gun makers to sell handguns in
the state for the first six months of that year. The state government faced a $1.1 million
start-up cost and another $750,000-a-year operating cost. New York's program began in
March 2001, with a state start-up expenditure of about $4.5 million. (No estimates are
available yet on New York's annual cost.)

In both states, the costs for dealers, gun makers, and prospective gun owners were
responsible for reducing handgun sales to law-abiding citizens. And what was the specific
benefit? Almost zero. The programs have not helped solve a single violent crime in either
state; they have so far been used only to identify two handguns stolen from a Maryland gun
shop.

A recent study by the State of California points to further practical difficulties
with ballistic fingerprinting. The study tested 790 pistols firing a total of 2,000
rounds. When the cartridges used with a particular gun came from the same manufacturer,
computer matching failed 38 percent of the time. When the cartridges came from different
manufacturers, the failure rate rose to 62 percent.

And this study does not even begin to address problems caused by wear, so the
real-world failure rate can be expected to be much higher. The California report warned
that "firearms that generate markings on cartridge casings can change with use and
can also be readily altered by the users." Further, it warned that the problems of
matching would soar dramatically if more guns were included in the sample. The study's
verdict: "Computer-matching systems do not provide conclusive results . . . potential
candidates [for a match must] be manually reviewed."

While registering guns by their ballistic fingerprints is a relatively new concept, we
have had plenty of experience using gun registration in general, and it has come up
woefully short. A couple of years ago, I testified before the Hawaii state legislature on
a bill to change registration requirements. Hawaii has had both registration and licensing
of guns for several decades.

In theory, if a gun is left at the crime scene, licensing and registration will allow
the gun to be traced back to its owner. Police have probably spent hundreds of thousands
of man-hours administering these laws in Hawaii. But despite this massive effort, there
has not been a single case in which police claimed that licensing and registration have
been instrumental in identifying a criminal.

The reason is simple. First, criminals very rarely leave their guns at a crime scene,
and when they do, it is because the criminals have been killed or seriously wounded.
Second — and more important for ballistic fingerprinting — would-be criminals
also virtually never get licenses or register their weapons. The guns that are recovered
at the scene are not registered.

Good intentions don't necessarily make good laws. What counts is whether the laws
actually work, and end up saving lives. On that measure, ballistic fingerprinting — a
useless diversion of valuable police resources — fails conspicuously, and it should
be opposed by anyone who wants to live in a safer society.